The present invention relates to a ceramic sintered body and a method of manufacturing the same, particularly, to a ceramic sintered body suitable for use in aircraft and space industries, gas turbines for power generation, gas turbines for automobiles, high temperature gas filters, etc., and a method of manufacturing the same.
A ceramic sintered body, which is superior to a metallic material in mechanical strength, heat resistance and wear resistance and is low in specific gravity, attracts attentions as a heat resistant construction material exposed to high temperatures. Among the various ceramic sintered bodies, oxide ceramic sintered bodies such as alumina, zirconia and magnesia and non-oxide ceramic sintered bodies such as carbide ceramic material like silicon carbide, nitride ceramic material like silicon nitride and boride ceramic material are under study for use as a heat resistant construction material.
The mechanical strength of the oxide ceramic sintered body, which is stable under an oxidizing atmosphere of room temperature, is rapidly lowered under high temperatures, making it difficult to use the oxide ceramic sintered body as a construction material exposed to high temperatures.
On the other hand, oxidation or decomposition tends to take place easily in the non-oxide ceramic sintered bodies such as the sintered bodies of the carbide ceramic material, the nitride ceramic material, and the boride ceramic material when these ceramic sintered bodies are exposed to an oxidizing atmosphere of high temperatures, leading to deterioration in the mechanical strength of the sintered body.
Japanese Patent Disclosure (KOKAI) No. 8-26815 discloses a rare earth-based composite oxide, comprising at least one ceramic crystal grain selected from the group consisting of a monosilicate represented by the general formula RE.sub.2 SiO.sub.5, where RE denotes a IIIa group element, and a disilicate represented by the general formula RE.sub.2 Si.sub.2 O.sub.7, where RE denotes a IIIa group element, and a complex oxide crystal grain represented by a general formula RE.sub.x M.sub.y O.sub.z, where RE denotes a IIIa group element, and M denotes at least one element selected from the group consisting of Al, Cr, Hf, Nb, Zr, Ti, V and Ta.
In the rare earth-based composite oxide disclosed in JP '815, the composite oxide represented by the general formula RE.sub.x M.sub.y O.sub.z is dispersed in the form of crystal grains within the crystal grains of the monosilicate and/or disilicate. Since any of these crystal grains is relatively large, the mechanical properties of the composite oxide are markedly deteriorated under high temperatures of 1,000 to 1,500.degree. C.